FIG. 7 is a side view in the stacking direction of a usual chalcopyrite solar cell 10. The chalcopyrite solar cell 10 is configured by disposing a first electrode layer 14 made of Mo, a light absorbing layer 16 made of Cu(InGa)Se (hereinafter, often referred to as CIGS), a buffer layer 18 made of CdS, ZnO, InS, or the like, and a transparent second electrode layer 20 made of ZnO/Al on a glass substrate 12 in this sequence. In FIG. 7, the reference numerals 22, 24 denote a first lead portion and a second lead portion, and lead wires 26, 28 are connected to the lead portions 22, 24.
In this way, the chalcopyrite solar cell 10 is a solar cell comprising a chalcopyrite compound which is typified by CIGS, as the light absorbing layer 16, and also called a I-III-VI cell.
When the chalcopyrite solar cell 10 is irradiated with light such as solar light, pairs of an electron and a hole are generated in the light absorbing layer 16. In the junction interface between the light absorbing layer 16 made of CIGS which is a P-type semiconductor, and the second electrode layer 20 of the N-type semiconductor, electrons gather in the interface of the second electrode layer 20 (N-type side), and holes gather in the interface of the light absorbing layer 16 (P-type side). Since this phenomenon occurs, an electromotive force is generated between the light absorbing layer 16 and the second electrode layer 20. The electric energy due to the electromotive force is taken out to the outside as a current from the first lead portion 22 and second lead portion 24 which are connected respectively to the first electrode layer 14 and the second electrode layer 20.
Usually, the chalcopyrite solar cell 10 is produced in the following manner. First, the first electrode layer 14 made of Mo is formed by sputtering or the like on the glass substrate 12 made of soda-lime glass or the like.
Next, as shown in FIG. 8, irradiation of a laser beam L is repeated while linearly scanning laser irradiation 30, and the first electrode layer 14 is divided into plural portions. This operation is called scribe.
After cutting dust produced in the division is removed away by washing, Cu, In, and Ga are deposited onto the first electrode layer 14 by sputtering film formation to dispose a precursor. The precursor is accommodated together with the glass substrate 12 and the first electrode layer 14 in a heat treatment furnace, and an annealing process is performed in an H2Se gas atmosphere. During the annealing process, selenization of the precursor occurs, and the light absorbing layer 16 made of CIGS is formed.
Next, the N-type buffer layer 18 made of CdS, ZnO, InS, or the like is disposed on the light absorbing layer 16. For example, the buffer layer 18 is formed by sputtering film formation, chemical bath deposition (CBD), or the like.
As shown in FIG. 9, a mechanical scribing process of linearly cutting the buffer layer 18 and the light absorbing layer 16 is performed by using a metal stylus 32. Namely, the buffer layer 18 and the light absorbing layer 16 are divided in a stripe manner by a mechanical technique.
Next, the second electrode layer 20 made of ZnO/Al is disposed by sputtering film formation. As shown in FIG. 10, thereafter, a mechanical scribing process of linearly cutting the second electrode layer 20, the buffer layer 18, and the light absorbing layer 16 is performed by using the metal stylus 32. As a result of the previous and present mechanical scribing processes, plural unit cells are disposed.
Finally, the first lead portion 22 and the second lead portion 24 are disposed in exposed portions of the first electrode layer 14 and the second electrode layer 20, respectively, thereby obtaining the chalcopyrite solar cell 10.
The chalcopyrite solar cell 10 which is obtained in this way has various advantages such as that the energy conversion efficiency is high, that photo-deterioration due to a secular change seldom occurs, that the radiation resistance is high, that the light absorption wavelength range is wide, and that the light absorption coefficient is large. Various researches for mass production of the solar cell have been conducted.
As described above, it is usual to select glass as the material of the substrate. The reasons of this are that glass is easily available and economical, that the surface is smooth, and hence the surface of a film stacked on the substrate can be made relatively smooth, and that sodium in glass disperses to the light absorbing layer 16 with the result that the energy conversion efficiency is high.
When the glass substrate 12 is used, however, the temperature during the selenization of the precursor cannot be set high. Therefore, it is difficult to advance the selenization to a composition at which the energy efficiency is very high. Since the substrate is thick, there are disadvantages that a feeding apparatus for feeding the glass substrate 12 during production of the chalcopyrite solar cell 10, and the like become large, and that the mass of the produced chalcopyrite solar cell 10 is large. Moreover, the glass substrate 12 is not substantially flexible, and hence it is difficult to apply a mass production method which is called a roll-to-roll process.
As a measure for solving the disadvantages, it is contemplated to change the material of the substrate to that other than glass. For example, Patent Reference 1 proposes a chalcopyrite solar cell in which a polymer film is used as a substrate. In addition, Patent Reference 2 proposes the use of stainless steel as a material of a substrate of a chalcopyrite solar cell, and Patent Reference 3 lists glass, alumina, mica, polyimide, molybdenum, tungsten, nickel, graphite, and stainless steel.    Patent Reference 1: JP-A-5-259494    Patent Reference 2: JP-A-2001-339081    Patent Reference 3: JP-A-2000-58893